BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to an imaging optical system such as an imaging lens
or a projector projection lens, and more particularly, to an imaging lens which is
appropriate for a wide-angle lens having a wide angle of view.
Description of the Related Art
[0002] In the related art, when a wide landscape is to be photographed by a camera, or when
a wide screen is to be projected within a short distance by a projector, a wide-angle
lens having a wide angle of view is used. A wide-angle lens can be used for an apparatus
where a distance between a reduction-side imaging plane and a lens end closest to
the reduction-side imaging plane is long. For example, a single-lens reflex camera
or a projector having a color combining system. For such applications, a wide-angle
lens will typically use a retrofocus-type lens unit. The retrofocus-type lens unit
is a lens unit with a lens having a strong negative refractive power disposed nearer
to an enlargement-side imaging plane than a stop. Hereinafter, the reduction-side
imaging plane side is referred to as the reduction-side; and the enlargement-side
imaging plane side is referred to the enlargement-side.
[0003] However, as the retrofocus-type lens unit has a wider angle of view, the diameter
of the enlargement-side lens is greatly increased. Techniques for solving the problem
are discussed in the English Abstract of Japanese Patent Application Laid-Open No.
04-356008 and
U.S. Patent Application Publication No. 2005/0117123.
[0004] The English Abstract of Japanese Patent Application Laid-Open No.
04-356008 discusses an optical system which forms an intermediate image of an object within
a lens unit and re-forms the intermediate image on an image plane. Hereinafter, in
order to avoid confusion in the specification, with respect to an in-lens conjugate
point where the intermediate image is formed within a lens unit as a division point,
the enlargement-side lens unit is referred to as a first lens unit, and the reduction-side
lens unit is referred to as a second lens unit.
[0005] The first lens unit in the lens unit discussed in the English Abstract of Japanese
Patent Application Laid-Open No.
04-356008 forms a reduced image of the object as an intermediate image by a reduction optical
system. The second lens unit is configured as a relay system which forms the intermediate
image on the image plane (an imaging plane of an image sensor). Accordingly, a back
focus of the first lens unit is shortened, so that the diameter of the enlargement-side
lens of the first lens unit is reduced.
[0006] The lens unit discussed in
U.S. Patent Application Publication No. 2005/0117123 is a projection lens for a projector, which forms an image obtained by a light modulation
element as an intermediate image and enlarges the intermediate image to project the
enlarged image onto a projection receiving surface. Therefore, similarly to the English
Abstract of Japanese Patent Application Laid-Open No.
04-356008, the diameter of the enlargement-side lens of the first lens unit is also reduced.
[0007] The English Abstract of Japanese Patent Application Laid-Open No.
2001-23887 discusses a projection optical system of an exposure apparatus, which forms an intermediate
image, although the projection optical system is not a wide-angle lens.
[0008] However, the lens unit discussed in the English Abstract of Japanese Patent Application
Laid-Open No.
04-356008 is a fisheye lens, and large distortion remains on a final image plane. Therefore,
the lens unit is not appropriate for a wide-angle lens for general picture photographing
or a projection lens for a projector, where distortion needs to be sufficiently corrected.
[0009] On the other hand, in the lens unit discussed in
U.S. Patent Application Publication No. 2005/0117123), although distortion is corrected, aberration correction is independently performed
in the first and second lens units disposed with respect to the in-lens conjugate
point as a division point. Therefore, although the diameter of the enlargement-side
lens is reduced, the total lens length is increased. In other words, both of the English
Abstract of Japanese Patent Application Laid-Open No.
04-356008 and
U.S. Patent Application Publication No. 2005/0117123 do not simultaneously accomplish the correction of distortion and the miniaturization
in the optical axis direction.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to an imaging optical system which forms an intermediate
image, the imaging optical system having a reduced size while sufficiently correcting
distortion.
[0011] According to a first aspect of the present invention, there is provided an imaging
optical system as specified in claims 1 to 12. According to a second aspect of the
present invention, there is provided a projection-type image display apparatus as
specified in claims 13 and 14. According to a third aspect of the present invention,
there is provided an image pickup apparatus as specified in claim 15.
[0012] According to an embodiment of the present invention, it is possible to provide an
imaging optical system which forms an intermediate image, the imaging optical system
having a reduced size while sufficiently correcting distortion, and a projection-type
image display apparatus and an image pickup apparatus using the imaging optical system.
[0013] Further features of the present invention will become apparent from the following
description of embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings, which are incorporated in and constitute a part of the
specification, illustrate embodiments, features, and aspects of the invention and,
together with the description, serve to explain the principles of the invention.
Fig. 1 is a cross-sectional view illustrating an optical system according to a first
embodiment of the present invention.
Fig. 2 illustrates longitudinal aberration graphs of the optical system according
to the first embodiment of the present invention.
Fig. 3 illustrates longitudinal aberration graphs at conjugate points in the optical
system according to the first embodiment of the present invention.
Fig. 4 is a cross-sectional view illustrating a case where the optical system according
to the first embodiment of the present invention is used for a projection-type image
display apparatus.
Fig. 5 is a cross-sectional view illustrating an optical system according to a second
embodiment of the present invention.
Fig. 6 illustrates longitudinal aberration graphs of the optical system according
to the second embodiment of the present invention.
Fig. 7 is a cross-sectional view illustrating an optical system according to a third
embodiment of the present invention.
Fig. 8 illustrates longitudinal aberration graphs of the optical system according
to a third embodiment of the present invention.
Fig. 9 is a cross-sectional view illustrating an optical system according to a fourth
embodiment of the present invention.
Fig. 10 illustrates longitudinal aberration graphs of the optical system according
to the fourth embodiment of the present invention.
Fig. 11 is a cross-sectional view illustrating an optical system according to a fifth
embodiment of the present invention.
Fig. 12 illustrates longitudinal aberration graphs of the optical system according
to the fifth embodiment of the present invention.
DESCRIPTION OF THE EMBODIMENTS
[0015] Various embodiments, features, and aspects of the invention will be described in
detail below with reference to the drawings.
[0016] Fig. 1 is a cross-sectional diagram illustrating a configuration including an imaging
lens (i.e. an imaging optical system) according to a first embodiment of the present
invention. The imaging optical system is a projection optical system, which is designed
for a projector (i.e. for a projection-type image display apparatus) . The imaging
optical system is a wide-angle lens which projects light beams modulated by a liquid
crystal panel 5 (a light modulation element) onto a screen (not illustrated) (a projection
receiving surface). The left side of Fig. 1 is an enlargement side, and the right
side thereof is a reduction side. The wide-angle lens illustrated in Fig. 1 is configured
to include a first lens unit 1 (a first optical unit) and a second lens unit 2 (a
second optical unit) in order from the enlargement side. The screen surface represents
an enlargement-side imaging plane, and the liquid crystal panel 5 is represents a
reduction-side imaging plane. Herein, in an enlargement projection apparatus like
a projector, an enlargement-side imaging plane is at a position where an image formed
by the light modulation element (the liquid crystal panel) is projected. In an image
pickup apparatus, the enlargement-side imaging plane is at a position of an object
to be imaged. In contrast, in the case of an enlargement projection apparatus, like
a projector and so on, the reduction-side imaging plane is the position where the
light modulation element (a liquid crystal panel) is provided. In the case of the
image pickup apparatus, the reduction-side imaging plane is the position where the
image pickup element, like, for example, a CCD, is provided.
[0017] The wide-angle lens according to the present embodiment comprises 20 lenses in total.
A prism glass 4 having no refractive power is disposed between a lens L20 closest
to the reduction side and the liquid crystal panel 5. The prism glass 4 is used for
color composition in the projector.
[0018] In Fig. 1, the dot-dashed line indicates the optical axis of the wide-angle lens.
An in-lens conjugate point 3 (intermediate image point) is located on the optical
axis between a tenth lens L10 and an eleventh lens L11. With respect to the in-lens
conjugate point 3 as a division point, the first lens L1 through the tenth lens L10
constitute the first lens unit 1, and the eleventh lens L11 through the final lens
L20 constitute the second lens unit 2.
[0019] The first lens unit 1 is configured to make the screen (an enlargement-side imaging
plane) and the in-lens conjugate point 3 conjugate to each other. The second lens
unit 2 is configured to make the in-lens conjugate point 3 and the liquid crystal
panel 5 (a reduction-side imaging plane) conjugate to each other. If the liquid crystal
panel 5 is set as a reference, the first lens unit 1 and the second lens unit 2 are
configured to make the liquid crystal panel 5 and the screen conjugate to each other,
and thus, the enlargement-side imaging plane can be called an enlargement-side conjugate
plane. Conversely, if the screen is set as a reference, the reduction-side imaging
plane can be called a reduction-side conjugate plane.
[0020] A numerical example of the present embodiment is listed as Numerical Example 1 as
follows. A surface number is a number uniquely designated to each lens surface in
order from the enlargement side; R is a radius of curvature of each lens surface,
d is a surface distance, and nd and νd are a refractive index and an Abbe number,
respectively, of a glass material at the d-line (587.56 nm). The lens surface with
the symbol "*" attached to the right side of the surface number denotes that the lens
surface has an aspherical shape according to the function described below, and coefficients
thereof are listed in the numerical example. Herein, a coordinate y is a coordinate
in the radial direction when the surface apex of the lens surface is set as a reference
and a coordinate x is a coordinate in the optical axis direction when the surface
apex of the lens surface is set as a reference. The object distance is infinite.
[0021] In addition, in numerical examples described hereinafter, a focal length of the entire
optical system of the wide-angle lens is denoted by an absolute value |f|. Since the
conjugate point is formed within a lens unit, the image of the final image plane is
an erected image. Therefore, in some cases, the focal length of the entire optical
system may have a negative value depending on the definition. However, since the refractive
power of the entire optical system is positive, the focal length is represented by
an absolute value. This is also applied to the other embodiments.
(Numerical Example 1)
[0022] |f| = 6.90 ω = 62.2° F/3.0 Image circle size ϕ26.2
Surface number |
R |
d |
nd |
νd |
OBJ |
∞ |
∞ |
|
|
1* |
63.814 |
3.92 |
1.820 |
42.7 |
2* |
13.659 |
4.35 |
|
|
3 |
16.654 |
3.61 |
1.772 |
49.5 |
4 |
8.111 |
5.77 |
|
|
5 |
1050.049 |
1.00 |
1.805 |
25.4 |
6 |
13.303 |
1.48 |
|
|
7 |
31.609 |
1.87 |
1.772 |
49.5 |
8 |
-295.242 |
0.50 |
|
|
9 |
31.218 |
13.76 |
1.772 |
49.5 |
10 |
-15.179 |
0.62 |
|
|
11 |
139.551 |
1.49 |
1.696 |
55.5 |
12 |
-15.540 |
1.24 |
1.805 |
25.4 |
13 |
10.662 |
3.23 |
1.563 |
60.6 |
14 |
-26.383 |
17.09 |
|
|
15 |
38.949 |
4.50 |
1.805 |
25.4 |
16 |
-107.135 |
0.29 |
|
|
17 |
18.445 |
6.02 |
1.805 |
25.4 |
18 |
40.195 |
19.01 |
|
|
19 |
-11.729 |
1.50 |
1.834 |
37.1 |
20 |
-166.339 |
2.55 |
|
|
21 |
-26.706 |
3.98 |
1.805 |
25.4 |
22 |
-20.649 |
0.50 |
|
|
23 |
-77.267 |
5.00 |
1.834 |
37.1 |
24 |
-20.071 |
0.50 |
|
|
25 |
64.062 |
2.16 |
1.834 |
37.1 |
26 |
2887.146 |
0.50 |
|
|
27 |
25.054 |
2.97 |
1.805 |
25.4 |
28 |
46.969 |
20.16 |
|
|
29 |
-13.250 |
2.00 |
1.487 |
70.2 |
30 |
-10.532 |
1.87 |
|
|
31 |
-10.068 |
2.26 |
1.805 |
25.4 |
32 |
25.857 |
6.75 |
1.651 |
58.5 |
33 |
-27.304 |
1.27 |
|
|
34 |
-213.988 |
5.78 |
1.487 |
70.2 |
35 |
-29.328 |
0.50 |
|
|
36* |
-625.000 |
10.00 |
1.755 |
51.1 |
37* |
-22.190 |
2.00 |
|
|
38 |
∞ |
30.00 |
1.516 |
64.1 |
39 |
∞ |
19.00 |
1.805 |
25.4 |
40 |
∞ |
|
|
|
IMG |
|
|
|
|
Surface number |
K |
A |
B |
C |
D |
E |
F |
1 |
0 |
6.371e-005 |
-2.364e-007 |
5.192e-010 |
-3.710e-013 |
-3.717e-016 |
9.1204e-019 |
2 |
0 |
1.631e-005 |
2.296e-007 |
-5.662e-009 |
5.797e-012 |
1.637e-013 |
-6.2823e-016 |
36 |
0 |
-2.317e-005 |
-4.911e-009 |
6.517e-011 |
-1.291e-013 |
-2.623e-016 |
7.3652e-019 |
37 |
0 |
1.296e-006 |
-1.537e-008 |
8.563e-011 |
-1.961e-013 |
2.242e-016 |
-1.5633e-019 |
[0023] Fig. 2 illustrates longitudinal aberration graphs representing an image forming performance
of the wide-angle lens according to the present embodiment. A spherical aberration
graph, an astigmatism graph, and a distortion graph are illustrated from the left
side of the figure. In the spherical aberration graph, a solid line indicates aberration
at the d-line (587.56 nm), a broken line indicates aberration at the F-line (486.13
nm), and a dotted line indicates aberration at the C-line (656.27 nm). The horizontal
axis denotes a defocus amount, and the scale thereof is -0.15 to +0.15 [mm]. In the
astigmatism graph, a solid line indicates curvature of field of a sagittal image plane,
and a dotted line indicates curvature of field of a meridional image plane. The horizontal
axis is the same as that of the spherical aberration graph. In the distortion graph,
the scale of the horizontal axis is -0.5 to +0.5 [%].
[0024] As illustrated in Fig. 2, it can be understood that distortion is corrected well.
In addition, spherical aberration and astigmatism are also corrected well.
[0025] In the wide-angle lens according to the present embodiment, spherical aberration,
curvature of field, and distortion still remain at the in-lens conjugate point 3.
Fig. 3 illustrates longitudinal aberration graphs at the in-lens conjugate point 3
according to the present embodiment. In Fig. 3, the view point is the same as that
of Fig. 2, but the scale is different from that of Fig. 2. The scale of the horizontal
axis of spherical aberration and astigmatism is -1.0 to +1.0 [mm] ; and the scale
of the horizontal axis of distortion is -5.0 to +5.0 [%]. It can be understood from
Fig. 3 that large curvature of field and large distortion remain at the in-lens conjugate
point 3. On the other hand, it can be understood that over-correction is made with
respect to axial chromatic aberration.
[0026] The lens closest to the enlargement side of the second lens unit 2, which is a relay
lens unit, is configured as a negative lens, and aberration opposite to the remaining
aberration is allowed to occur, so that the aberration is cancelled. Therefore, good
image forming performance illustrated in Fig. 2 is obtained in the final image plane.
In addition, curvature of field and distortion are allowed to remain at the in-lens
conjugate point 3, so that a lens for aberration correction of the first lens unit
1 does not need to be installed. Therefore, the wide-angle lens according to the present
embodiment can be configured with a small number of lenses. In addition, it is possible
to miniaturize the wide-angle lens according to the present embodiment in the optical
axis direction.
[0027] In addition, in the first lens unit 1, particularly negative distortion is allowed
to remain, so that the diameter of the lens for distortion correction does not need
to be large. Therefore, the diameter of the enlargement-side lens can be greatly reduced.
In addition, the distance between the most-reduction-side lens surface and the liquid
crystal panel 5 can be shortened.
[0028] As described above, in the wide-angle lens according to the present embodiment, the
correction of aberration of the intermediate image formed at the in-lens conjugate
point 3 is performed by the second lens unit 2. At this time, as the wide-angle lens
has a wider angle of view, negative distortion greatly occurs. Particularly, as the
image height is increased, high-order negative distortion occurs as illustrated in
Fig. 3. Therefore, the second lens unit 2 needs to generate strong positive distortion.
[0029] Accordingly, in the imaging lens according to the present embodiment, although the
wide-angle lens has a wider angle of view, or although the image height is high, the
above-described effect can be obtained by arranging a surface having strong negative
refractive power to be disposed at the first refractive surface sf of the enlargement
side of the negative lens at the side (enlargement side) closest to the in-lens conjugate
point 3 of the second lens unit 2. The surface having strong negative refractive power
has a function of bending (bouncing) the light beam which may be bent toward an inner
side of the first lens unit 1 greatly to an outer side thereof and a function of bending
the light beam having a particularly high image height greatly to the outer side.
Therefore, high-order positive distortion can be generated.
[0030] In other words, the wide-angle lens according to the present embodiment is configured
to include a first optical unit having positive refractive power which forms an intermediate
image and a second optical unit having positive refractive power which forms the intermediate
image on the image plane. In addition, since a lens disposed closest to the enlargement
side of the second optical unit is a negative lens, it is possible to sufficiently
correct distortion and to provide a miniaturized imaging lens.
[0031] In addition, when the focal length of the first lens unit 1 is fF and the focal length
of the second lens unit 2 is fR, the wide-angle lens according to the present embodiment
satisfies the following condition:
[0032] More desirably, instead of the condition (A1), the wide-angle lens may satisfy the
following condition:
[0034] The condition (1a) is the ratio of the focal length f1 of the negative lens L11 disposed
closest to the enlargement side of the second lens unit 2 to the focal length fR of
the second lens unit 2.
[0035] The condition (2a) is the ratio of the focal length f1 to the focal length |f| of
the entire optical system of the wide-angle lens (the entire optical system including
the first lens unit 1 and the second lens unit 2).
[0036] The condition (3a) is the ratio of the focal length f1 to the focal length fF of
the first lens unit 1.
[0037] The condition (4a) is the ratio of the radius of curvature r of the first refractive
surface sf of the enlargement side of the negative lens L11 disposed closest to the
enlargement side of the second lens unit 2 to the focal length |f| of the entire optical
system of the wide-angle lens.
[0038] The condition (5a) is the ratio of a refractive power r/(n-1) of the first refractive
surface sf of the second lens unit 2 to the focal length fR1 of a first group of the
second lens unit 2. n is a refractive index of the negative lens L11. Herein, the
first group of the second lens unit 2 denotes a lens or a lens group disposed at the
enlargement side with respect to the largest lens surface distance in the second lens
unit 2.
[0039] In the numerical ranges of the conditions (1a) to (5a), if the numeric value is smaller
than the lower limit value or if the numeric value is larger than the upper limit
value, distortion including high order distortion cannot be appropriately corrected.
[0041] The numeric values in the various embodiments are listed in Table 1.
[0042] More desirably, off-axis principal rays incident on the first refractive surface
sf may be set to converge at the reduction side. In other words, a converging light
flux may be incident on the negative lens L11. Accordingly, it is possible to allow
high-order positive distortion to more effectively occur, and it is possible to suppress
an increase in diameter of the enlargement side lens of the second lens unit 2.
[0043] In addition, a positive lens L12 is disposed at the reduction side of the negative
lens L11 having the first refractive surface sf without another negative lens interposed
therebetween, and the positive lens L12 may be a meniscus lens having a shape convex
toward the reduction side. Accordingly, while distortion occurring at the first refractive
surface sf remains, the diverged rays can be returned to the direction where the rays
are to converge.
[0044] More desirably, in the imaging lens having a particularly large degree of wide angle
(first, second, and fourth embodiments), when the focal length of the negative lens
L11 having the refractive surface sf is denoted by f1 and the focal length of the
positive lens L12 is denoted by f2, the following condition (6a) may be satisfied:
[0045] More desirably, instead of the condition (6a), the following condition (6b) may be
satisfied:
[0046] In the conditions (6a) and (6b), if the numeric value is smaller than the lower limit
value, the focal length of the positive lens L12 is too greatly increased in comparison
to the focal length of the negative lens L11 (the refractive power of the positive
lens becomes weak in comparison to the negative lens), so that the effect of allowing
the rays of the positive lens L12 to converge cannot be obtained. On the other hand,
in the conditions (6a) and (6b), if the numeric value is larger than the upper limit
value, the effect of distortion intentionally occurring at the negative lens L11 cannot
be obtained.
[0047] The numeric values in the various embodiments are listed in Table 1.
[0048] More desirably, since the aberration correction effect can be more effectively obtained,
the distance between the reduction-side surface of the negative lens L11 having the
refractive surface sf and the enlargement side surface of the positive lens L12 may
be an air distance. In other words, the negative lens L11 and the positive lens L12
can be adjacent to each other.
[0049] More desirably, the second lens unit 2 can have a magnification close to the unit
magnification if possible. The reason is as follows. If the second lens unit has the
unit magnification, the paths of off-axis principal rays become symmetric at the enlargement
side and the reduction side of an edge portion of a stop or a lens substantially functioning
as a stop, so that off-axis aberration such as coma or curvature of field can be easily
corrected.
[0050] In addition, in the present embodiment, a cemented lens SL1 obtained by cementing
three lens L6, L7, and L8 is disposed in the first lens unit 1. In a lens unit where
imaging is performed twice, axial chromatic aberration greatly occurs in comparison
to the lens unit where imaging is performed once. In order to solve this problem,
as described above, a three-lens element cemented lens obtained by cementing positive,
negative, and positive lenses in this order from the enlargement side is used. This
configuration is very effective for reducing axial chromatic aberration.
[0051] As the present embodiment, when a three-lens cemented lens is used in the first lens
unit, the negative lens L7 may be configured by using a high dispersion glass, and
the positive lenses L6 and L8 may be configured by using a low dispersion glass. In
the cemented lens SL1, the glass material of the negative lens L7 has lower Abbe number
(higher dispersion) than the glass material of the positive lenses L6 and L8. Accordingly,
axial chromatic aberration is effectively reduced.
[0052] Fig. 4 is a diagram illustrating shifting (moving) of a projection image 47 projected
on a screen when the wide-angle lens according to the present embodiment is used as
a projection lens PL of a projection-type image display apparatus. The projection-type
image display apparatus is configured to include a driving unit (not illustrated)
which moves the projection lens PL in a direction having a component perpendicular
to the optical axis of the projection lens to shift the projection position of the
projection image 47 projected on the screen. In order to shift the projection image
47 projected on the screen, the first lens unit 1 or the second lens unit 2 is not
individually moved, but the entire optical system of the lens units is shifted. In
addition, the moving direction of the projection lens PL is opposite to the moving
direction of the projection image. Accordingly, the projection image can be appropriately
shifted. In other words, the shifting direction of the liquid crystal panel 46 (a
light modulation element) is the same as the shifting direction of the projection
image 47.
[0053] Fig. 5 is a cross-sectional diagram illustrating a configuration of a wide-angle
lens according to a second embodiment of the present invention. The wide-angle lens
is designed by considering the use as an imaging lens (imaging optical system) of
an image pickup apparatus such as a single-lens reflex camera. The first lens unit
1 is configured to include a first lens L1 through an eleventh lens L11. The second
lens unit 2 is configured to include a twelfth lens L12 through a final lens L20.
In the second embodiment, the lens corresponding to the negative lens L11 according
to the first embodiment is a lens L12.
[0054] The left side of Fig. 5 is the enlargement side, and the right side thereof is the
reduction side. The wide-angle lens illustrated in Fig. 5 is configured to include
a first lens unit 1 (first optical unit) and a second lens unit 2 (second optical
unit) in this order from the enlargement side. The object plane is an enlargement-side
imaging plane; and the image plane is a reduction-side imaging plane.
[0055] The image pickup apparatus include an image sensor. In the image pickup apparatus,
an image plane is an imaging plane of the image sensor, which receives light from
a subject (object) through the wide-angle lens and photo-electrically converts the
received light to form image data.
[0056] The first lens unit 1 is configured to make the object plane and an in-lens conjugate
point 3 conjugate to each other. The second lens unit 2 is configured to make the
in-lens conjugate point 3 and the image sensor conjugate to each other.
[0057] In addition, unlike the first embodiment, the back focus region of the image pickup
apparatus is a movable region of a flip-up mirror (quick-return mirror) and a prism
glass is not disposed there. A numerical example of the present embodiment is listed
as Numerical Example 2. The object distance is infinite.
[0058] The imaging lens according to the second embodiment is also configured to satisfy
the condition (A1) described in the first embodiment, and the lens disposed closest
to the enlargement side of the second lens unit is configured as a negative lens.
Therefore, it is possible to sufficiently correct distortion and to provide a miniaturized
imaging lens.
[0059] In addition, the imaging lens according to the second embodiment is also configured
to satisfy the desirable conditions described in the first embodiment, and thus, similar
effects obtained in the conditions of the first embodiment can be also obtained.
(Numerical Example 2)
[0060] |f| = 10 ω = 65.2° F/3.0 Image circle size ϕ43.28
|
R |
d |
nd |
νd |
OBJ |
∞ |
∞ |
|
|
1* |
82.062 |
6.54 |
1.820 |
42.7 |
2* |
25.431 |
8.37 |
|
|
3 |
34.122 |
6.50 |
1.834 |
42.7 |
4 |
9.881 |
7.99 |
|
|
5 |
-281.802 |
1.65 |
1.583 |
59.3 |
6 |
21.303 |
1.72 |
|
|
7 |
141.145 |
6.25 |
1.805 |
25.4 |
8 |
-51.360 |
5.59 |
|
|
9 |
-53.433 |
3.62 |
1.696 |
55.5 |
10 |
-15.998 |
0.50 |
|
|
11 |
62.078 |
3.46 |
1.677 |
55.3 |
12 |
-13.466 |
1.65 |
1.805 |
25.4 |
13 |
15.441 |
3.88 |
1.563 |
60.6 |
14 |
-29.361 |
13.34 |
|
|
15 |
29.411 |
8.28 |
1.696 |
55.5 |
16 |
-47.572 |
0.20 |
|
|
17 |
15.310 |
7.16 |
1.808 |
22.7 |
18 |
117.677 |
1.14 |
|
|
19 |
-96.471 |
4.69 |
1.805 |
25.4 |
20 |
16.052 |
5.54 |
|
|
21 |
-13.428 |
1.50 |
1.737 |
32.2 |
23 |
-16.967 |
8.05 |
1.805 |
25.4 |
24 |
-15.696 |
0.20 |
|
|
25 |
287.024 |
7.51 |
1.834 |
42.7 |
26 |
-27.300 |
0.20 |
|
|
27 |
27.696 |
6.14 |
1.834 |
37.1 |
28 |
355.764 |
1.00 |
|
|
29 |
18.817 |
2.00 |
1.698 |
30.1 |
30 |
13.870 |
5.36 |
|
|
31 |
-20.188 |
2.48 |
1.720 |
34.7 |
32 |
13.455 |
6.35 |
1.496 |
81.5 |
33 |
-49.220 |
0.20 |
|
|
34 |
16.251 |
5.67 |
1.496 |
81.5 |
35 |
-27.774 |
1.96 |
|
|
36* |
-20.455 |
1.89 |
1.497 |
81.5 |
37* |
-18.954 |
|
|
|
IMG |
|
|
|
|
Surface number |
K |
A |
B |
C |
D |
E |
F |
1 |
0 |
2.082e-005 |
-2.462e-008 |
2.015e-011 |
-7.073e-015 |
-3.932e-018 |
2.9057e-021 |
2 |
0 |
2.018e-005 |
3.638e-008 |
-2.757e-010 |
3.566e-014 |
7.412e-016 |
-7.2652e-019 |
36 |
0 |
7.359e-005 |
1.620e-006 |
-3.839e-009 |
-6.492e-011 |
1.915e-013 |
0 |
37 |
0 |
1.433e-004 |
1.592e-006 |
1.125e-009 |
-6.884e-011 |
5.055e-013 |
0 |
[0061] Fig. 6 illustrates longitudinal aberration graphs representing image forming performance
according to the present embodiment. Similarly to the first embodiment, a particularly
wide angle and high performance can be obtained.
[0062] Fig. 7 is a cross-sectional diagram illustrating a configuration of a wide-angle
lens according to a third embodiment of the present invention. In the configuration
of the present embodiment, the back focus is increased by allowing the angle of view
to be slightly suppressed and allowing the F-number to be smaller. A numerical example
of the present embodiment is listed as Numerical Example 3. The object distance is
infinite.
[0063] In the third embodiment, the lens corresponding to the negative lens L11 according
to the first embodiment is a lens L9.
[0064] The wide-angle lens according to the third embodiment is also configured to satisfy
the condition (A1) described in the first embodiment, and the lens disposed closest
to the enlargement side of the second lens unit is configured as a negative lens.
Therefore, it is possible to sufficiently correct distortion and to provide a miniaturized
imaging lens.
[0065] In addition, the wide-angle lens according to the third embodiment is also configured
to satisfy the desired conditions described in the first embodiment, and thus, similar
effects obtained in the conditions of the first embodiment can be also obtained
(Numerical Example 3)
[0066] |f| = 12.4 ω = 37.2° F/2.0 Image circle size ϕ18.8
|
R |
d |
nd |
νd |
OBJ |
∞ |
∞ |
|
|
1* |
23.948 |
4.85 |
1.693 |
53.2 |
2* |
7.010 |
3.30 |
|
|
3 |
13.156 |
2.21 |
1.805 |
25.4 |
4 |
24.194 |
1.38 |
|
|
5 |
-227.645 |
6.00 |
1.688 |
31.0 |
6 |
10.261 |
4.33 |
1.788 |
47.3 |
7 |
-18.411 |
9.56 |
|
|
8 |
-11.847 |
1.48 |
1.805 |
25.4 |
9 |
708.273 |
1.90 |
|
|
10 |
-22.312 |
3.73 |
1.772 |
49.5 |
11 |
-12.013 |
0.50 |
|
|
12 |
-81.905 |
3.83 |
1.772 |
49.5 |
13 |
-22.103 |
0.50 |
|
|
14 |
55.880 |
3.97 |
1.696 |
55.5 |
15 |
-69.760 |
35.78 |
|
|
16 |
-13.289 |
7.00 |
1.772 |
49.5 |
17 |
-19.179 |
1.23 |
|
|
18 |
-67.392 |
5.14 |
1.696 |
55.5 |
19 |
-29.305 |
0.50 |
|
|
20 |
26.402 |
6.13 |
1.834 |
42.7 |
21 |
78.428 |
28.29 |
|
|
22 |
-12.813 |
4.78 |
1.805 |
25.4 |
23 |
107.016 |
0.85 |
|
|
24 |
-53.535 |
3.24 |
1.805 |
25.4 |
25 |
29.655 |
7.80 |
1.487 |
70.2 |
26 |
-9.547 |
1.10 |
1.755 |
27.5 |
27 |
-17.122 |
0.50 |
|
|
28 |
-80.069 |
4.88 |
1.595 |
67.7 |
29 |
-17.861 |
2.49 |
|
|
30 |
46.209 |
3.72 |
1.808 |
22.7 |
31 |
-148.016 |
1.50 |
|
|
32 |
∞ |
31.74 |
1.516 |
64.1 |
33 |
∞ |
7.50 |
1.516 |
64.1 |
34 |
∞ |
19.50 |
1.805 |
25.4 |
35 |
∞ |
|
|
|
IMG |
|
|
|
|
Surface number |
K |
A |
B |
C |
D |
E |
1 |
-5.609e+000 |
3.441e-005 |
-3.798e-007 |
9.898e-010 |
-6.188e-012 |
1.010e-014 |
2 |
-4.544e-001 |
8.402e-005 |
-1.196e-007 |
-1.241e-008 |
4.265e-010 |
-9.531e-012 |
[0067] Fig. 8 illustrates longitudinal aberration graphs representing image forming performance
according to the present embodiment.
[0068] A three-lens cemented lens SL2 is disposed in the second lens unit according to the
present embodiment. The three-lens cemented lens SL2 is configured so that a lower-dispersion
negative lens is interposed between higher-dispersion positive lenses. The three-lens
cemented lens SL2 has a strong achromatic effect. In addition, the three-lens cemented
lens SL2 can be configured to include, in order from the enlargement side, in this
order from the enlargement side, a biconcave negative lens, a biconvex positive lens,
and a negative meniscus lens having a concave surface facing the enlargement side.
[0069] Fig. 9 is a cross-sectional view illustrating a configuration of a wide-angle lens
according to a fourth embodiment of the present invention. The fourth embodiment is
different from the first embodiment in that focusing is performed by moving a sixth
lens 91, which is the sixth lens from the enlargement side of the second lens unit
2, as a focus lens. The sixth lens 91 has a weak negative refractive power. During
focusing from an infinitely distant point to a closest point, the sixth lens 91 is
moved along the optical axis from the reduction side to the enlargement side. The
focus lens, which is moved for performing focusing, may a single lens or a lens group
(focus group) including a plurality of lenses.
[0070] A numerical example of the present embodiment is listed as Numerical Example 4. The
letter "z" affixed to the numeric value of the surface distance denotes that the surface
distance varies according to a change in object distance. In the last portion of the
numerical example, listed is the numeric value of the surface distance according to
a change in the object distance.
[0071] In the fourth embodiment, the lens corresponding to the negative lens L11 according
to the first embodiment is a lens L11.
[0072] The wide-angle lens according to the fourth embodiment is also configured to satisfy
the condition (A1) described in the first embodiment, and the lens disposed closest
to the enlargement side of the second lens unit is configured as a negative lens.
Therefore, it is possible to sufficiently correct distortion and to provide a miniaturized
imaging lens.
[0073] In addition, the wide-angle lens according to the fourth embodiment is also configured
to satisfy the desirable conditions described in the first embodiment, and thus, similar
effects obtained in the conditions of the first embodiment can be also obtained.
(Numerical Example 4)
[0074] |f| = 6.89 ω = 62.1° F/3.0 Image circle size ϕ26.2
|
R |
d |
nd |
νd |
OBJ |
∞ |
667.00z |
|
|
1* |
83.035 |
3.33 |
1.768 |
49.2 |
2* |
13.997 |
4.90 |
|
|
3 |
18.992 |
3.23 |
1.799 |
29.8 |
4 |
8.723 |
5.55 |
|
|
5 |
-237.318 |
1.01 |
1.784 |
26.2 |
6 |
14.347 |
1.41 |
|
|
7 |
41.907 |
1.70 |
1.772 |
49.5 |
8 |
-726.137 |
0.50 |
|
|
9 |
28.677 |
12.60 |
1.772 |
49.5 |
10 |
-15.734 |
1.56 |
|
|
11 |
79.794 |
1.61 |
1.696 |
55.5 |
12 |
-10.728 |
1.00 |
1.805 |
25.4 |
13 |
10.306 |
1.94 |
1.563 |
60.6 |
14 |
-34.894 |
11.00 |
|
|
15 |
-184.875 |
2.53 |
1.799 |
29.8 |
16 |
-28.022 |
0.20 |
|
|
17 |
20.765 |
4.02 |
1.805 |
25.4 |
18 |
390.472 |
7.06 |
|
|
19 |
∞ |
9.19 |
|
|
20 |
-12.985 |
1.50 |
1.805 |
25.4 |
21 |
-99.493 |
5.10 |
|
|
22 |
-17.029 |
5.07 |
1.805 |
25.4 |
23 |
-15.357 |
0.50 |
|
|
24 |
457.856 |
6.09 |
1.772 |
49.5 |
25 |
-35.370 |
1.52 |
|
|
26 |
944.629 |
2.95 |
1.805 |
25.4 |
27 |
-75.396 |
0.50 |
|
|
28 |
62.959 |
3.27 |
1.805 |
25.4 |
29 |
1070.925 |
23.01 |
|
|
30 |
∞ |
3.66z |
|
|
31 |
-87.951 |
1.00 |
1.487 |
70.2 |
32 |
-162.164 |
7.82z |
|
|
33 |
-12.686 |
2.36 |
1.799 |
29.8 |
34 |
39.274 |
5.46 |
1.772 |
49.5 |
35 |
-31.754 |
0.50 |
|
|
36 |
67.885 |
7.51 |
1.496 |
81.5 |
37 |
-32.069 |
0.50 |
|
|
38* |
-625.000 |
7.32 |
1.677 |
54.8 |
39* |
-22.773 |
2.00 |
|
|
40 |
∞ |
30.00 |
1.516 |
64.1 |
41 |
∞ |
19.00 |
1.805 |
25.4 |
42 |
∞ |
|
|
|
IMG |
|
|
|
|
Surface number |
K |
A |
B |
C |
D |
E |
F |
1 |
0 |
6.893e-005 |
-2.472e-007 |
5.381e-010 |
-3.802e-013 |
-4.379e-016 |
7.3562e-019 |
2 |
0 |
1.807e-006 |
3.830e-007 |
-5.955e-009 |
3.466e-012 |
1.604e-013 |
-5.7934e-016 |
38 |
0 |
-1.890e-005 |
-1.774e-008 |
2.406e-011 |
-2.501e-014 |
7.008e-017 |
0 |
39 |
0 |
7.924e-006 |
-2.017e-008 |
7.022e-011 |
-1.408e-013 |
3.292e-016 |
0 |
|
Closest Point |
Middle Point |
Infinitely distant Point |
OBJ |
667.00 |
400.00 |
1000.00 |
d30 |
3.66 |
9.39 |
0.85 |
d32 |
7.82 |
2.10 |
10.64 |
[0075] Paths of light rays are greatly changed according to a subject distance (object distance)
in the case of a particularly-wide-angle lens as in the present embodiment, or according
to a projection distance in the case of a projection lens. Therefore, there is a problem
in that various aberrations are changed due to focusing. In order to perform focusing
while suppressing a change in aberration if possible, a plurality of lenses needs
to be moved during focusing, that is, floating needs to be performed. However, there
is still a problem in that the change in aberration cannot be completely suppressed.
[0076] From the review of focusing of the lens where the in-lens conjugate point 3 is formed
according to the present embodiment, it is found that the change in aberration is
still large in the method for moving the entire first lens unit or the entire second
lens unit. In this type of lens, the first lens unit 1 and the second lens unit 2
generate aberration in opposite directions to perform the aberration correction. Therefore,
if the first lens unit 1 and the second lens unit 2 are independently moved, the change
in aberration cannot be suppressed. On the other hand, since the first lens unit 1
is a retrofocus-type lens unit, the change in aberration may be suppressed to some
degree by using the method for simultaneously moving a plurality of lens groups, which
is called floating as described above. However, since distortion is changed, distortion
cannot be sufficiently corrected, wherein the sufficient distortion correction is
an object of the present embodiment.
[0077] Therefore, in the present embodiment, the change in aberration including distortion
can be effectively suppressed by using the method for performing focusing by moving
a portion of lenses of the second lens unit 2. In particular, in the second lens unit
2, it is desirable to move a lens having a weak refractive power in the vicinity of
the light ray with the lowest image height. The reason is as follows. If the lens
located at the position where the height of a light ray is low is allowed to be moved,
the change in various off-axis aberrations due to the movement is suppressed. Therefore,
the change in curvature of field or distortion can be suppressed to be almost zero.
In other words, focusing is performed by moving a portion of lenses of the second
lens unit 2, so that it is possible to greatly solve the problem of changes in aberration
due to focusing changes.
[0078] Herein, when a focal length of the focus lens (entire optical system of the focus
lens group in the case of a plurality of lenses) is denoted by f
fo, the following condition may be satisfied:
[0079] More desirably, instead of the condition (7a), the following condition may be satisfied:
[0080] In the conditions (7a) and (7b), if the numeric value is smaller than the lower limit
value of the numeric range, the refractive power of the focus lens is strengthened,
and thus it is difficult to suppress a change in aberration. On the other hand, if
the numeric value is larger than the upper limit value of the numeric range, the refractive
power is weakened, and the moving amount is increased during focusing, so that the
size of the lens is greatly increased. In the present embodiment, the focal length
f
fo of the focus lens is -394.8 [mm], and |f
fo/f| = 57.3.
[0081] Fig. 10 illustrates longitudinal aberration graphs representing image forming performance
according to the present embodiment. It can be understood that a change in various
aberrations can be suppressed down to an infinitesimal level over the range of a closest
point to an infinitely distant point. Although the example in which a single focus
lens is moveable is described in the present embodiment, the embodiment is not limited
to the example, but a focus lens group including a plurality of lenses may be moveable.
In this case, if the focus lens described in the present embodiment is configured
as a focus lens group, the same effect as that in the present embodiment can be obtained.
[0082] Fig. 11 is a cross-sectional view illustrating a configuration of a wide-angle lens
according to a fifth embodiment of the present invention. The fifth embodiment is
different from the third embodiment in that a zoom lens is configured as a five-group
configuration including five lens groups which are moved with the distance being changed
during zooming. In the present embodiment, the first lens group B1 and the fifth lens
group B5 are configured to be stationary during zooming, and the second lens group
B2, the third lens group B3, and the fourth lens group B4 are configured to move during
zooming.
[0083] A numerical example of the present embodiment is listed as Numerical Example 5. The
letter "z" affixed to the numeric value of the surface distance denotes that the surface
distance is changed in accordance with zooming. In the last portion of the numerical
example, listed is the numeric value of the surface distance according to zooming.
[0084] In the fifth embodiment, the lens corresponding to the negative lens L11 according
to the first embodiment is a lens L9.
[0085] The wide-angle lens according to the fifth embodiment is also configured to satisfy
the condition (A1) described in the first embodiment, and the lens disposed closest
to the enlargement side of the second lens unit (the third lens group B3) is configured
as a negative lens. Therefore, it is possible to sufficiently correct distortion and
to provide a miniaturized imaging lens.
[0086] In addition, the wide-angle lens according to the fifth embodiment is also configured
to satisfy the desirable conditions described in the first embodiment, and thus, similar
effects obtained in the conditions of the first embodiment can be also obtained.
(Numerical Example 5)
[0087] |f| = 12.5 to 13.9 ω = 37 to 34° F/2.0 to 2.1 Image circle size ϕ18.8
|
R |
d |
nd |
νd |
OBJ |
∞ |
∞ |
|
|
1* |
11.731 |
2.38 |
1.677 |
54.8 |
2* |
6.147 |
5.37 |
|
|
3 |
16.570 |
5.21 |
1.799 |
29.8 |
4 |
130.697 |
1.42 |
|
|
5 |
-39.422 |
6.00 |
1.612 |
37.0 |
6 |
11.401 |
5.65 |
1.772 |
49.5 |
7 |
-28.798 |
2.24z |
|
|
8 |
∞ |
1.47 |
|
|
9 |
∞ |
4.47 |
|
|
10 |
-9.175 |
1.86 |
1.698 |
30.1 |
11 |
-236.127 |
1.49 |
|
|
12 |
-28.694 |
4.52 |
1.772 |
49.5 |
13 |
-11.784 |
0.50 |
|
|
14 |
-150.946 |
4.33 |
1.772 |
49.5 |
15 |
-23.677 |
1.63z |
|
|
16 |
44.020 |
4.01 |
1.696 |
55.5 |
17 |
-154.312 |
12.60 |
|
|
18 |
∞ |
15.55 |
|
|
19 |
∞ |
8.78 |
|
|
20 |
-12.964 |
6.30 |
1.805 |
25.4 |
21 |
-20.184 |
0.50 |
|
|
22 |
-79.437 |
6.31 |
1.772 |
49.5 |
23 |
-26.803 |
5.84z |
|
|
24 |
25.089 |
5.79 |
1.733 |
51.4 |
25 |
94.021 |
11.28 |
|
|
26 |
∞ |
11.15 |
|
|
27 |
-17.106 |
4.02 |
1.805 |
25.4 |
28 |
39.895 |
1.07 |
|
|
29 |
-51.285 |
6.30 |
1.799 |
29.8 |
30 |
23.544 |
7.78 |
1.487 |
70.2 |
31 |
-10.252 |
1.60 |
1.761 |
26.5 |
32 |
-16.281 |
3.53 |
|
|
33 |
-576.999 |
5.72 |
1.595 |
67.7 |
34 |
-21.736 |
0.50z |
|
|
35 |
33.403 |
2.85 |
1.808 |
22.7 |
36 |
73.744 |
3.00 |
|
|
37 |
∞ |
31.74 |
1.516 |
64.1 |
38 |
∞ |
7.50 |
1.516 |
64.1 |
39 |
∞ |
19.50 |
1.805 |
25.4 |
40 |
∞ |
|
|
|
IMG |
Surface number |
K |
A |
B |
C |
D |
E |
1 |
-2.685e + 000 |
-2.336e-005 |
-1.960e-007 |
3.509e-009 |
-2.113e-011 |
4.005e-014 |
2 |
-7.281e-001 |
-1.890e-004 |
-4.630e-010 |
-1.110e-009 |
7.618e-011 |
-9.632e-013 |
|
Wide-Angle End |
Telephoto End |
d7 |
2.24 |
4.27 |
d15 |
1.63 |
0.50 |
d23 |
5.84 |
0.50 |
d34 |
0.50 |
4.93 |
[0088] In the lens type where the in-lens conjugate point 3 is formed according to the present
embodiment, as described in the fourth embodiment, aberrations in the optical systems
in front of and behind the in-lens conjugate point 3 are in a trade-off relation.
Therefore, if only the one-side optical system is moved during zooming, aberration
balance is changed, so that a change in aberration is increased. Accordingly, in the
present embodiment, the second lens group B2 and the third lens group B3 are configured
to be simultaneously moved, so that the aberration balance is maintained. In addition,
the third lens group B3 is further moved, so that a change in position of an image
plane caused by zooming of the third lens group B3 can be suppressed. Therefore, the
zooming function is mainly performed by the second lens group B2 and the fourth lens
group B4.
[0089] Fig. 12 illustrates longitudinal aberration graphs representing image forming performance
according to the present embodiment. It is understood that basic image performance
is maintained even when zooming is performed.
[0091] While the present invention has been described with reference to embodiments, it
is to be understood that the invention is not limited to the disclosed embodiments.
STATEMENTS
[0092]
- 1. An imaging optical system comprising:
a first optical unit having positive refractive power for making an image at an image
plane at an enlargement-side of the imaging optical system and an intermediate image
at an intermediate image position in the imaging optical system conjugate to each
other; and
a second optical unit having positive refractive power for making the intermediate
image and an image at an image plane at a reduction-side of the imaging optical system
conjugate to each other,
wherein, when a focal length of the first optical unit is denoted by fF and a focal
length of the second optical unit is denoted by fR, the following condition is satisfied:
and
wherein the second optical unit comprises a negative lens disposed on the optical
axis closest to the enlargement side.
- 2. The imaging optical system according to statement 1, wherein, when a focal length
of the negative lens is denoted by f1, the following condition is satisfied:
- 3. The imaging optical system according to any preceding statement, wherein, when
a focal length of the negative lens is denoted by f1 and a focal length of the entire
optical system including the first and second optical units is denoted by |f|, the
following condition is satisfied:
- 4. The imaging optical system according to any preceding statement, wherein, when
a focal length of the negative lens is denoted by f1, the following condition is satisfied:
- 5. The imaging optical system according to any preceding statement, wherein an enlargement-side
surface of the negative lens has a shape convex toward the reduction side, and
wherein, where a radius of curvature of the enlargement-side surface of the negative
lens is denoted by r and a focal length of the entire optical system including the
first optical unit and the second optical unit is denoted by |f|, the following condition
is satisfied:
- 6. The imaging optical system according to any preceding statement, wherein the enlargement-side
surface of the negative lens has a shape convex toward the reduction side, and
wherein, when a radius of curvature of the enlargement-side surface of the negative
lens is denoted by r, a refractive index of the negative lens is denoted by n, and
a focal length of a lens or a lens group disposed at the enlargement side with respect
to the largest surface distance in the second optical unit is denoted by fR1, the
following condition is satisfied:
- 7. The imaging optical system according to any preceding statement, operable to perform
focusing by moving a portion of the second optical unit as a focus group.
- 8. The imaging optical system according to statement 7, wherein, when a focal length
of the focus group is denoted by ffo and a focal length of the entire optical system including the first optical unit
and the second optical unit is denoted by |f|, the following condition is satisfied:
- 9. The imaging optical system according to statement 7 or 8, wherein a lens in the
focus group has the smallest diameter of any of the lenses in the second optical unit.
- 10. The imaging optical system according to any one of statements 7 to 9, wherein
the focus group is arranged so that it is moved from the reduction side to the enlargement
side during focusing from infinity to a closest focusing distance.
- 11. The imaging optical system according to any preceding statement, further comprising
a positive lens disposed at the reduction side of the negative lens,
wherein the positive lens is disposed at a position adjacent to the negative lens,
wherein, when a focal length of the negative lens is denoted by f1 and a focal length
of the positive lens is denoted by f2, the following condition is satisfied:
- 12. The imaging optical system according to any preceding statement, wherein the imaging
optical system is configured to form an image from light received from an object at
the enlargement side imaging plane on an image sensor at the reduction side imaging
plane.
- 13. A projection-type image display apparatus comprising:
a light modulation element; and
the imaging optical system according to any preceding statement,
wherein the imaging optical system is a projection optical system configured to project
an image by projecting an image formed from light from the light modulation element
at the reduction side imaging plane onto a projection receiving surface at the enlargement
side imaging plane.
- 14. The projection-type image display apparatus according to statement 13, further
comprising means for moving the imaging optical system in a direction giving a component
of movement of the imaging optical system perpendicular to its optical axis, and
arranged so that upon moving the imaging optical system the projected image is moved
in a direction opposite to the moving direction of the imaging optical system.
- 15. An image pickup apparatus comprising:
an image sensor; and
the imaging optical system according to statement 12.
1. An imaging optical system comprising:
a first optical unit having positive refractive power for making an image plane at
an enlargement-side of the imaging optical system and an intermediate image conjugate
to each other; and
a second optical unit having positive refractive power for making the intermediate
image and an image plane at a reduction-side of the imaging optical system conjugate
to each other,
characterized in that,
a lens located at a most-enlargement-side of the second optical unit is a negative
lens,
when a focal length of the first optical unit is denoted by fF, a focal length of
the second optical unit is denoted by fR and a focal length of the negative lens is
denoted by f1,
the following condition is satisfied:
2. The imaging optical system according to claim 1,
characterized in that,
when a focal length of the negative lens is denoted by f1 and a focal length of the
second optical unit is denoted by fR , the following condition is satisfied:
3. The imaging optical system according to claim 1 or 2,
characterized in that,
when a focal length of the negative lens is denoted by f1 and a focal length of the
entire optical system including the first and second optical units is denoted by f,
the following condition is satisfied:
4. The imaging optical system according to any one of claims 1 to 3,
characterizing in that,
an enlargement-side surface of the negative lens has a shape convex toward the reduction
side, and
where a radius of curvature of the enlargement-side surface of the negative lens is
denoted by r and a focal length of the entire optical system including the first optical
unit and the second optical unit is denoted by f, the following condition is satisfied:
5. The imaging optical system according to any one of claims 1 to 4, charactering in
that
the enlargement-side surface of the negative lens has a shape convex toward the reduction
side, and
when a radius of curvature of the enlargement-side surface of the negative lens is
denoted by r, a refractive index of the negative lens is denoted by n, and a focal
length of a lens or a lens group disposed at the enlargement side with respect to
the largest surface distance in the second optical unit is denoted by fR1, the following
condition is satisfied:
6. The imaging optical system according to any one of claims 1 to 5, characterizing in that, it is operable to perform focusing by moving a portion of the second optical unit
as a focus group.
7. The imaging optical system according to claim 6,
characterizing in that, when a focal length of the focus group is denoted by ffo and a focal length of the
entire optical system including the first optical unit and the second optical unit
is denoted by f, the following condition is satisfied:
8. The imaging optical system according to claim 6 or 7, charactering in that, the focus
group includes a lens having the smallest diameter in the second optical unit.
9. The imaging optical system according to any one of claims 6 to 8, charactering in
that, the focus group is arranged so that it is moved from the reduction side to the
enlargement side during focusing from infinity to a closest focusing distance.
10. The imaging optical system according to any one of claims 1-9, characterizing in that, at least one lens in each of the first optical unit and the second optical unit
moves during zooming.
11. The imaging optical system according to any one of claims 1-10, characterizing in that, off-axis principal rays incident on the enlargement-side surface of the negative
lens by approaching to the optical axis.
12. The imaging optical system according to any one of claims 1 to 11, further comprising
a positive lens disposed at the reduction side of the negative lens, characterized in that the positive lens is disposed at a position adjacent to the negative lens.
13. The imaging optical system according to claim 12, characterizing in that, the positive lens is a meniscus lens having a shape convex toward the reduction
side.
14. The imaging optical system according to claim 12 or 13,
characterizing in that,
when the focal length of the negative lens is denoted by f1 and the focal length of
the positive lens is denoted by f2, the following condition is satisfied: